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85 lines
2.7 KiB
Markdown
85 lines
2.7 KiB
Markdown
| Supported Targets | ESP32 | ESP32-C3 | ESP32-S2 | ESP32-S3 |
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| ----------------- | ----- | -------- | -------- | -------- |
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# Non-Volatile Storage (NVS) Read and Write Example
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(See the README.md file in the upper level 'examples' directory for more information about examples.)
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This example demonstrates how to read and write a single integer value using NVS.
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In this example, value which is saved holds the number of ESP32 module restarts. Since it is written to NVS, the value is preserved between restarts.
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Example also shows how to check if read / write operation was successful, or certain value is not initialized in NVS. Diagnostic is provided in plain text to help track program flow and capture any issues on the way.
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Detailed functional description of NVS and API is provided in [documentation](https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/storage/nvs_flash.html).
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Check another example *storage/nvs_rw_blob*, which shows how to read and write variable length binary data (blob).
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## How to use example
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### Hardware required
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This example does not require any special hardware, and can be run on any common development board.
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### Build and flash
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Build the project and flash it to the board, then run monitor tool to view serial output:
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```
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idf.py -p PORT flash monitor
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```
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(To exit the serial monitor, type ``Ctrl-]``.)
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See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
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## Example Output
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First run:
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```
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Opening Non-Volatile Storage (NVS) handle... Done
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Reading restart counter from NVS ... The value is not initialized yet!
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Updating restart counter in NVS ... Done
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Committing updates in NVS ... Done
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Restarting in 10 seconds...
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Restarting in 9 seconds...
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Restarting in 8 seconds...
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Restarting in 7 seconds...
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Restarting in 6 seconds...
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Restarting in 5 seconds...
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Restarting in 4 seconds...
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Restarting in 3 seconds...
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Restarting in 2 seconds...
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Restarting in 1 seconds...
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Restarting in 0 seconds...
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Restarting now.
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```
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Subsequent runs:
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```
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Opening Non-Volatile Storage (NVS) handle... Done
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Reading restart counter from NVS ... Done
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Restart counter = 1
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Updating restart counter in NVS ... Done
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Committing updates in NVS ... Done
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Restarting in 10 seconds...
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Restarting in 9 seconds...
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Restarting in 8 seconds...
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Restarting in 7 seconds...
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Restarting in 6 seconds...
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Restarting in 5 seconds...
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Restarting in 4 seconds...
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Restarting in 3 seconds...
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Restarting in 2 seconds...
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Restarting in 1 seconds...
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Restarting in 0 seconds...
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Restarting now.
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```
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Restart counter will increment on each run.
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To reset the counter, erase the contents of flash memory using `idf.py erase-flash`, then upload the program again as described above.
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